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Silicon dioxide (SiO2) is deposited at between 300 and 450C (depending on needs... ie metals 300C), low pressure (~350 mtorr), from silane and oxygen with or without phosphine doping. Doped LTO is also called PSG, or phosphosilicate glass). The refractive index of the film depends on the phosphorous content, lower deposition rate. The refractive index is also influenced by the temperature of the deposition. The oxide deposition rate is mostly dependent on the temperature and is ~ 175A/min at 400C for 4 inch wafers (~200A/min for 3 inch wafers).

Tylan LPCVD Furnace Operation (short)

  1. Clean substrates
    Diffusion clean with HF last
  2. Enable the furnace
  3. Verify Pump program running
    Go to the furnace and use the STATUS button to verify that the system is in 'RUN' mode and running the ?PUMP program?.
  4. End Pump program
    ALARM ACK twice
  5. Verify the Tube is vented
    Ten minutes after the pump program has ended you must manually test that the tube is vented. Push MANUAL on the boat puller, push FAST, then LOOK AT THE TUBE while you hold down OUT. You should immediately see the boat start to come out. If it does not, stop and wait 10 more minutes and test it again.
  6. Load your program (only after verifying manually that tube is vented)
    From TYCOM type "LO  <program name>  <furnace#>" <RET>.  You will be asked to enter the deposit time.
  7. Run program
  8. Load your wafers.
    The first boat (as the boats come out of the furnace) is for dummies. The second boat is the clean non-metal boat.  The third boat is the metal boat.  The fourth boat (the last one to come out of the tube) is a dummy boat.  Both dummy boats should have 4 to 6 wafers.  The two middle boats should have 13 wafers each.
  9. Send in tube
    ALARM ACK once
  10. Monitor furnace
    Take pressure readings during the gross leak check, leak check and the deposition steps of the program and write the values in the logbook.
  11. Unload wafers
  12. End program
    ALARM ACK twice
  13. Load pump program
  14. Run Pump program
  15. Measure wafers and log results
  16. Disable the furnace


Uniformity Testing Procedure for TylanBPSG LTO


To provide a standard procedure to monitor oxide thickness and uniformity both wafer-to-wafer over a 26 wafer load and within-a-wafer.

Deposition material: Silicon dioxide

Expected deposition thickness: 2700 A


Frequency of test

To be completed after major maintenance such as a tube change or on a set schedule to be determined or as needed based on user feedback.


Documentation of results

To be posted in Badger.




  • Use six new 'L' test wafers; <100>, P-type (boron), 10-20 ohm-cm.
  • Clean at wbdiff in the following sequence; 5:1:1 H2O:H2O2:NH4OH ten minutes, rinse, 5:1:1 DI;HCl:H2O2 ten minutes, rinse, 50:1 DI:HF 30 sec, rinse, spin dry.
  • Load program LTO400PC into TylanBPSG. Time variable is 00:20:00.
  • The boats must be loaded with dummies (13 wafers in each, loaded every other slot) at all times to ensure uniform wafer to wafer deposition.
  • Using very clean tweezers or vacuum wand replace the dummy wafers with cleaned test wafers the following positions with flats up:
    1st boat (Front) in the 5th slot.
    1st boat in the 13th.
    1st boat in the 21st slot.
    2nd boat (Back) in the 5th slot.
    2nd boat in the 13th.
    2nd boat in the 21st slot.
  • Measure:

    Use Woollam to measure silicon dioxide thickness across each wafer in nine locations with floating index of refraction using procedure Silicon Oxide (100 - 10,000 Ang).  record the average thickness, standard deviation, and index of refraction at 633nm. Test sites should be no more than about 15mm from the edge of the wafer.


    Record results on Badger. If test values are not within 10% of plotted test average, contact the Diffusion Process/Maintenance team.
    Save wafers in a box with the date, furnace number, program name and growth time.  They may be re-tested sometime in the future.


    TylanBPSG LTO Qualification Results


    4-5-11 TylanBPSG qual

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